Figure 4. Inhibition of human neutrophil elastase by variants Spn4F–Spn4H.

Progress curves were recorded by measuring the cleavage of MeOSuc-AAPV-AMC (91 μM) by human neutrophil elastase in the presence of Spn4F, Spn4G or Spn4H. The apparent first order rate constant k′ for each curve was plotted against the inhibitor concentration (inset). From the slope of the linear regression line k_assoc was calculated using eqn (2). The enzyme was used at concentrations of 1 (Spn4F and Spn4G) or 0.5 nM (Spn4H).